Subject: Re: [BUG] cpufreq: constant cpu_khz
From: Peter Zijlstra <peterz@infradead.org>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, Dave Jones <davej@codemonkey.org.uk>,
       linux-kernel <linux-kernel@vger.kernel.org>, cpufreq@vger.kernel.org,
       Alok Kataria <akataria@vmware.com>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <20080825112244.34b2fe67@infradead.org>
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	 <20080825175547.GA26131@codemonkey.org.uk> <20080825175712.GA10848@elte.hu>
	 <20080825112244.34b2fe67@infradead.org>
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Date: Mon, 25 Aug 2008 21:27:10 +0200
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On Mon, 2008-08-25 at 11:22 -0700, Arjan van de Ven wrote:
> On Mon, 25 Aug 2008 19:57:12 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
> 
> > 
> > * Dave Jones <davej@codemonkey.org.uk> wrote:
> > 
> > >  > hm, that too is due to the tsc.c unification - Alok Cc:-ed.
> > >  > Applied your fix to x86/urgent.
> > > 
> > > ACKed-by: Dave Jones <davej@redhat.com>
> > > 
> > > Good catch Peter.  I'm puzzled how that bug was latent on 64bit for
> > > so long with no-one realising though.
> > 
> > i think it's the combination of these two factors:
> > 
> >  - bootup frequently is typically full-speed, so we calibrate things 
> >    right
> > 
> >  - cpufreq events are relatively slow-scale - and when they trigger
> > the system is definitely not under load. So how precisely the
> > scheduler functions isnt all that important in such scenarios -
> > there's tons of CPU power available.
> > 
> 
> - many many of the 64 bit capable cpus are constant-tsc anyway

Ironically I noticed it first on 64bit ;-)


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